Titanium nitride is a known barrier material used to prevent spiking of aluminum contacts into a silicon substrate. Titanium nitride can be deposited by sputtering; either by sputtering a layer of titanium in the presence of nitrogen gas, or, preferably, a contact layer of titanium is deposited first and a layer of titanium nitride sputtered thereover. Since the initial titanium layer sputtered in argon contains no impurities, the contact resistance is not adversely affected. However, untreated titanium nitride barrier layers can only be used to prevent spiking of an overlying aluminum contact layer below temperatures of about 350-450.degree. C.
Thus it is also known to enhance the barrier properties of titanium nitride by annealing or incorporating oxygen into the film. The oxygen fills the spaces between the grain boundaries of the titanium nitride. Annealing can be carried out in a Rapid Thermal Anneal (RTA) chamber, or by heating in a nitrogen atmosphere containing oxygen. This is known as "stuffing" the titanium nitride layer. Such titanium nitride barrier layers can be heated above the flow temperature of aluminum contacts, thus permitting the aluminum to be heated sufficiently to flow in contact openings, ensuring that the openings are completely filled and that voids are not present.
As substrate wafer sizes become larger, and devices made in the wafers become smaller and are placed closer together, many problems have arisen in filling small openings with material in a conformal manner that avoids the formation of voids. As the aspect ratio of openings becomes higher (the ratio of width to depth) it becomes more difficult to fill openings by sputtering.
Liao et al, in an article entitled "Ti/TiN Barrier Enhancement for Aluminum Plug Interconnect Technology", VMIC Conf. 1994 ISMIC-103/94 pp 428-434, disclosed an RTA treatment of a sputtered, low density titanium/titanium nitride stack, which formed a TiON layer at the titanium/titanium nitride interface. Their suggested process requires sputtering 550 .ANG. of titanium in the contact opening first, followed by sputtering 500 .ANG. of titanium nitride. These depositions can be carried out in the same chamber. However, the wafers are then exposed to air and heated to 650.degree. C. in an RTA chamber, which requires a break in the vacuum and transfer of the substrate to an RTA chamber prior to the deposition of the aluminum contact layer. This extra step and extra transfer of the substrate reduces the throughput of the system and thus increases the costs of producing the contact. Further, we have found that this process does not completely eliminate aluminum spiking.
Ho et al, U.S. Pat. No. 5,232,871, describe the preparation of TiN barrier layers for MOS devices which are said to prevent aluminum contacts from interdiffusion or spiking into an underlying silicon layer. The TiN layer can be annealed or can be treated with an oxygen plasma that reacts with the titanium nitride layer. Aluminum is then sputter deposited, possibly in the same cluster tool. The annealing step or the oxygen plasma treatment require a separate annealing or plasma process chamber, which requires an additional transfer of the wafer, and thus increases the cost and decreases the throughput of this process.
Thus efforts to provide improved titanium nitride barrier layers with improved barrier properties and that can be operated in a continuous manner using a minimum number of processing chambers at low cost have continued.